1. Field of the Invention
The invention relates to an improved method of and apparatus for measuring exhaust gas with charged particles, in particular in a motor vehicle.
2. Prior Art
Devices for measuring exhaust gas with charged particles are known in the prior art. They are used in conjunction with combustion processes, especially in motor vehicles. Besides the determination of chemical components such as oxygen or carbon dioxide, it is important to obtain measurements of the particle concentration, the exhaust gas quantity, or the exhaust gas flow speed, so as to make optimal variation of the combustion process possible. It is also known at present, in motors, to employ external exhaust gas recirculation to reduce the emissions of nitrogen oxides. To make it possible for the parameters of the exhaust gas to be determined as precisely as possible, direct measurement in the exhaust gas course is advantageous. The often-used hot-film air flow rate meter can be employed under only very limited conditions here, however, since it is only limitedly tolerant of soiling from exhaust gas. It must be noted that if the exhaust gas recirculation rate is determined with an error of even only about 1%, the result can be miscalculation of the NOx or soot emissions of approximately 3% to 5%. Moreover, with large volumetric throughputs, it is more difficult to implement the hot-film air flow rate meter. A good principle for solving the problem of determining particles in the exhaust gas stream is shown in German Patent Disclosure DE 102 42 301 A1, where an ionizing device charges particles in the exhaust gas stream, and these charged particles are detected downstream in the exhaust gas stream by a charge measuring device. The more charged particles are detected, the higher the particle concentration.